One might not expect a butcher in rural Greece to recognise Costas Lapavitsas. He is, after all, an economist, a professor at the School of Oriental and African Studies in London. His research interests include the evolution and function of the Japanese financial system and his books include The Political Economy of Money and Finance – probably not staples of discussion among rural Greek butchers.

But when, just before Easter, the Lapavitsas went shopping for groceries in Kopanos ("A godforsaken village," apparently, "ugly as hell"), said butcher spotted his name. "I know of a Costas Lapavitsas," he said. "I have seen him in a video on the internet." On being told that video star and customer were one and the same, the butcher responded with more excitement than is desirable from someone wielding a cleaver: "Ah, Debtocracy!"

Lapavitsas does have a star turn in Debtocracy, a film whose success is as unlikely as the academic's celebrity. It's a documentary about the financial crisis that has struck Greece; the collapse of public finances; the €110bn loan from Europe and the International Monetary Fund; and the savage spending cuts to come.

Unlike other entries to the nascent credit-crunch movie genre, the film-makers do not go looking for guilty men and women. No Inside Job, this. Instead what you get is a polemic against the European system; an explanation of how Greece was always doomed to struggle against the likes of Germany. "So are we the black sheep of an all-successful Europe?" asks the voiceover. "Or has the system been ailing since its youth?"

Debtocracy makes a compelling case that the entire euro system was rotten from the start, with bankers in Frankfurt and Paris left with piles of surplus cash, and southern Europeans getting by on cheap loans. Made on a budget of €8,000 (£7,110) and with very little flashy camera work or fancy use of archive, this is still – I can confidently say, without delving too far into history – the best film of Marxian economic analysis yet produced.

Stuck up on a website and YouTube in early April, Debtocracy has garnered something close to a million views and has been broadcast on small Greek television channels, gradually building an audience. "At first, it was young Greeks with broadband connections," says Aris Chatzistefanou – who co-wrote and co-directed the film with Katerina Kitidi. "But then we heard stories of how small villages were screening it, and how old men in the countryside were asking their sons to download it on to DVDs." In the process, the film has become an artefact in the popular resistance to the austerity package imposed on Greece – and across southern Europe. In Portugal, the Left Bloc put on a showing of Debtocracy in a small cinema to launch its recent election campaign. The film was also scheduled to be screened to 4,000 protesters in Barcelona's Plaza Catalunya before the authorities broke up proceedings.

When I speak to Chatzistefanou, he is still recovering from showing his film in the central Syntagma square in Athens. The screening only got going at 2.30am "and then the audience wanted to discuss it. We still had 400 people arguing over the Greek financial crisis at five in the morning."

Timing has a lot to do with Debtocracy's success. Greece's economy has sunk deeper into crisis, buttressing the film's argument that the nation is being broken, not fixed, by the IMF and the eurozone. Yet the film's suggestion that Greeks should renegotiate, and refuse to pay some of its ruinous debts, still barely features in mainstream Greek politics or media. Which leaves one video on the internet to be passed around a swelling band of dissenters.

After returning from Kopanos to London, Lapavitsas received an email: "Greetings from the village!" began the butcher. "I just want to congratulate you on your film. When you come back we can have a proper discussion."